Stonewashing of cotton and cotton blend fabrics has gained great popularity and provides many styling applications in today's apparel market. This effect is chiefly applied to denim products but may be applied to cotton goods treated with vat, sulfur, reactive, direct and naphthol dyes, as well as pigments. Typically ring dyed yarns are woven and are then normally treated according to various so-called "stonewashing" processes that may or may not include abrasive materials to remove portions of the outer blue dyed yarns partially exposing the white portion of the yarn underneath. Stonewashing is costly and time consuming. The term "stone washing" and related descriptions herein refers to the use of abrasive stones such as pumice, cellulase enzymes or other treatments used to abrade fabrics or garments.
The traditional procedure for providing a stonewashed appearance to garments is to expose the garment, typically denim jeans, to a combination of bleaching and an abrasive material. This combination provides a faded, worn appearance and is achieved by tumbling the garments with an abrasive substance, typically pumice stones and usually also with a bleaching solution such as potassium permanganate, a chlorine-based bleach or the like. Typically the garment to be stonewashed is denim or other type of cotton fabric or a predominantly cotton garment in which the cotton yarn is ring dyed. When examined in cross section, the cotton fibers of the ring dyed yarn are dyed only around the outer circumference of the cotton yarn leaving the center portion or core undyed, hence the term "ring dyed" when the yarns are viewed in cross section. Removal, such as by abrasion or other means, of a portion of the ring dyed outer surface of the yarn will leave the undyed portion exposed to view thus giving the faded appearance of a garment that has been worn for a considerable period of time. Abrasive treatment also imparts a worn, weathered appearance. In addition, the stonewashing process softens the hand of the garment giving it a more comfortable, less rigid, familiar feel and comfort when worn.
Conventional stonewashing procedures are time consuming and costly and provide garments which sometimes vary from batch to batch. In addition, stonewashing is usually performed on finished garments, that is garments in the completely constructed or fabricated condition. It would be desirable to provide a procedure that assures more uniform results prior to actual construction of the garment.
Stonewashed cotton fabrics with best washed appearance are usually woven from ring spun yarns that are ring dyed. Indigo dye tends to dye the outside of the fiber bundle in a ring spun cotton yarn or fabric without penetrating into the core of the yarn or body of the fabric. When the dyed surface is worn or abraded away (e.g., in a washing machine with stones or a combination of stones and cellulose enzyme), such ring dyeing allows the inner white areas to show through. It is more difficult to achieve this effect when using cotton yarns made on open end spinning systems which are looser in cross section and therefore are more easily penetrated during dyeing, increasing the time needed to achieve the desired stone washing result.
The present invention achieves the desired worn, stonewashed appearance of ring dyed denim and other types of woven cellulosic fabrics from open end spun yarns by providing a controlled penetration of the indigo dye into the surface of the yarn and/or fabric such that further processing, primarily stonewashing or simulated stonewashing, will result in the desired level of exposure of the undyed fibers to provide the appropriate stonewashed fabric appearance in a shorter period of time or at a reduced cost or, preferably, both. We call this procedure of dyeing "RL" in the following description of the process and end results.